The present application is directed to a process for the removal of impurities from natural gas condensate, and particularly, to a process for the removal of mercury from natural gas condensate.
Natural gas which is produced from a natural gas well is typically separated into components, which are in turn purified to provide products for a variety of end uses. The high-pressure mixture produced from the well, i.e., the wellstream, is typically sent to a separator vessel or a series of separator vessels maintained at progressively lower pressures where the wellstream is separated into a gaseous fraction and a liquid fraction.
The gaseous fraction leaving the separator, which may contain the impurities mercury, carbon dioxide and hydrogen sulfide, is sent to a gas treatment and purification plant where typically the mercury concentration is reduced to &lt; 0.1 micrograms/m.sup.3, the CO.sub.2 concentration is reduced to the parts per million (ppm) level, and the H.sub.2 S to about one (1) ppm.
The liquid fraction is typically preheated, e.g., to 150.degree. C., to affect partial vaporization and is then separated, for example, in a stabilizer column. In the upper section of the stabilizer column, the stream is rectified, i.e., the heavy hydrocarbons are removed from the vapor phase, and in the lower section of the stabilizer column, the liquid stream is stripped of its light hydrocarbon components. Complete stabilization can be further enhanced by heating the bottom liquid stream of the stabilizer column in a reboiler. The reboiler supplies additional heat in order to reduce the light hydrocarbon content of the liquid. The stabilizer column produces two streams, a stream which leaves the top of the stabilizer column containing low molecular weight hydrocarbons, e.g., C.sub.1 -C.sub.4, and other gases and a stabilized condensate stream which leaves the bottom of the stabilizer column.
It has been found that the mercury in wellstreams from gas producing wells which contain mercury is partitioned among the gaseous and liquid streams. This mercury is thought to originate from the geologic deposits in which the natural gas is entrapped.
Typical steps for the processing of the liquid fraction of the wellstream do not reduce the amount of mercury in the liquid fraction leaving the separator. For example, a liquid fraction leaving the separator(s) having a mercury content of about 220 .mu.g/kg(ppb) will yield a stabilized condensate containing about 220 .mu.g/kg(ppb). The presence of this mercury in a natural gas condensate is undesirable and can cause damage to downstream processing equipment.
Equipment damage may result when mercury accumulates in equipment constructed of various metals, especially aluminum, by forming an amalgam with the metal. For example, in the production of ethylene, a natural gas condensate is commonly passed through a heat exchanger constructed of aluminum. Such equipment exists in the section of the ethylene manufacturing facilities where ethylene is separated from hydrogen, ethane and other hydrocarbons by chilling. It has been found that mercury tends to amalgamate with the aluminum of which the heat exchanger is constructed thereby creating the risk of corrosion cracking with potentially catastrophic results.